This invention relates to plugging a hole in an object, and particularly to a plug, inserting tool and the method for plugging an unused coolant passage or the like in an injection molding die.
In almost all cases where a product is manufactured by forming it in a die or mold, the die body will incorporate drilled passages for a liquid cooling or heating medium. This is true in injection plastic molding, injection rubber molding and metal die casting. In thermoform and die casting processes, the die is cooled by a liquid medium, usually water, in the drilled passages. In thermoset processes, the die is heated by hot oil or steam circulated through the drilled passages.
With only the exception of a drilled passage with an inlet and outlet on its two openings, all interconnecting drilled passages must have some provision for plugging unused openings to prevent external leaking. Further, when a labyrinth pattern is formed in the die body by intersecting a passage with three or more perpendicular passages, some form of diverting plug is used to cause the liquid to flow in the prescribed flow path.
General prior practice among tool and die makers is to seal an unused external opening with a threaded pipe plug. This is a secure and effective solution, although it requires machine time to form the threads.
An alternative to the pipe plug is a threadless pressure plug, which has a screw that squeezes and expands an O-ring. This approach has the advantage of eliminating the time necessary to machine threads. However, the expansion plug is considerably more expensive than a pipe plug.
In those cases where internal passages are plugged to divert the liquid flow, there are a number of prior products or techniques used in the tool and die trade to seal the unused passages. The threadless expansion plug is often used, although it is complicated to position and tighten. In a blind hole, that is, where there is access only from one end, the die maker must be careful not to press it further into the hole beyond the position where it is desired.
More commonly used are plug-and-spacer arrangements wherein a slip-fit plug blocks the drilled passage and is positioned by small diameter rods. In some applications, the tool and die shop may manufacture its own spool shaft by reducing the diameter of a slip-fit rod in those areas where flow is desired. Each of the present designs has inherent limitations. In the case of plug-and-spacer arrangements, the seal around the plug is never complete. Because the drilled passage is rough, clearance is required to push the plug to the required depth. The resulting leakage past the plug area may be sufficient to alter the liquid flow, especially when the flow is restricted at the manifold valves to control die temperature. Further, the small diameter rods used in the flow area can accrete liquid-borne contaminants causing an eventual accumulation which can restrict or plug the entire passage system. The time required to manufacture and fit a plug-and-spacer diverting system is also a factor to be considered, especially when machining is required.
Accordingly, it is the general object of the present invention to provide a plug for sealing a hole in an object, particularly a coolant passage in an injection molding die, a tool for inserting the plug, and a method of so doing.
A further object is to provide such a plug which is easily and accurately positionable in a blind hole.
Another object is to provide a plug which is very simple to manufacture at low cost.
A further object is to provide an inserting tool for the plug which is able to be operated from only one end of a hole.
Still another object is to provide such a tool which accurately places the plug at the desired location in the hole.
A still further object is to provide a method or system of installing the plugs of the present invention.
These and other objects and advantages of the present invention and the manner in which they are achieved will be made apparent as the specification and claims proceed, taken in conjunction with the drawings which illustrate the preferred embodiment.